The father of an unarmed man shot and killed by a Chicago police officer over the summer called Wednesday for Cook County State's Attorney Anita Alvarez to bring criminal charges against the officer.

Speaking with a microphone at Daley Plaza while flanked by nearly two dozen supporters, Emmett Farmer urged Alvarez to prosecute Officer Gildardo Sierra for murder in the fatal shooting of his son, Flint, in West Englewood on June 7.

The Tribune ran a front-page article last month about Sierra, a nine-year veteran who shot three people while on duty between January and June. Two of them died.

Flint Farmer, 29, was holding a cellphone when Sierra fired 16 shots at him, hitting him seven times, according to autopsy and police records. A deputy medical examiner who performed the autopsy viewed a video of the shooting — captured by a police car video camera — and said it was evident that Farmer was on the ground when the fatal final shots were fired by Sierra.

The Tribune reported the FBI is investigating the shooting. Flint Farmer's girlfriend has filed a lawsuit on behalf of their daughter against the city and Sierra.

Sierra, who has declined comment, was responding to a call of a domestic squabble between Farmer and his girlfriend. He told police detectives that he feared for his life because he believed Farmer had a weapon. Police said weapons were recovered at the two earlier shootings involving Sierra, but not in Farmer's case.

"I think it's really cut and dried … He shot and killed my son," the elder Farmer declared. "He needs to be arrested. He needs to be tried. He needs to be found guilty and sent to jail for murder."

The elder Farmer, wife Carolyn and a handful of the followers walked to Alvarez's downtown office to meet with her, but staffers said she was unavailable. He handed over part of a police report concerning his son's shooting and the Tribune article to pass along to Alvarez.

The state's attorney's office wouldn't confirm or deny if it is investigating any of Sierra's shootings.

"But we would remind the public that the Cook County state's attorney's office actively investigates all referrals of criminal conduct by police officers that we receive from our state and federal investigative partners," the office said in a statement.